This invention relates to injection molding and more particularly to an improved method of manufacturing an integral heater nozzle for an injection molding system.
As has been long known, the provision of heat and the heat transfer characteristics of a heater nozzle is critical to its satisfactory operation. More recently, the rapidly increasing use of difficult to mold engineering materials such as flame retardant, glass filled polycarbonate and nylons has made the characteristics of corrosion and wear resistance of more and more importance. Thus heater nozzles are required which provide improved combinations of these characteristics, while remaining economically feasible to produce. The applicant's U.S. Pat. No. 3,383,493 which issued May 14, 1968 shows a heater block which is pressure cast of a beryllium copper alloy. While this has been very satisfactory for many applications, it increasingly is being found not to be sufficiently corrosion and wear resistant for the complete range of uses to which it is being applied. The applicant's U.S. Pat. No. 4,238,671 which issued Dec. 9, 1980 discloses a heated sprue bushing which overcomes this problem by providing an inner core portion through which the melt flows formed of a beryllium nickel alloy which is quite corrosion resistant. However, this structure has the disadvantages that it is relatively costly to manufacture and the beryllium nickel alloy is very difficult to machine. Other attempts to overcome the problem include nickel plating the melt passage through heater blocks of the type shown in the applicant's above-mentioned U.S. Pat. No. 3,383,493. However, it has been found that materials such as polycarbonate can have a gripping force when it shrinks sufficient to strip off this type of corrosion resistant plating and ruin the heater nozzle. Consequently, it is desirable to provide a heater nozzle which is sufficiently durable for modern materials, while retaining the necessary heat transfer characteristics.